1. Field of the Invention
The present invention relates generally to a connection establishing method in broadcasting packet communication and a packet communication system having a function of automatically shunting or branching a broadcasting packet and more particularly, to a method and a system which can realize suitable broadcasting packet communication and also can eliminate any load concentration to a particular module or port, which might undesirably occur in a so-called broadcasting packet communication in which a common packet is transferred from a packet terminal to a plurality of destination packet terminals at the same time, thereby to prevent any local overload.
2. Description of the Related Art
FIG. 1 shows, as an example, the internal arrangement of a packet switching node in a packet switching network.
The packet switching node of FIG. 1 includes a plurality of terminal interfaces 10 (11, 12, . . . and 1n) provided as associated with packet terminals and to perform data exchange between these packet terminals and the present packet switching node, a plurality of line interfaces 20 (21, 22, . . .) provided as associated with multiplexing lines in the packet switching network and to perform data exchange between these multiplexing lines and the associated packet switching node, an interrupt control bus BUS1, a control bus BUS2, an access control bus BUS3, a data bus BUS4, these buses being provided as intra-node buses between these terminal and line interfaces 10 and 20, a node controller 30 provided to generally control the terminal and line interfaces 10 and 20 to synthetically control the packet packet switching operation required every time in the node, and a bus access controller 40 provided to receive data-bus BUS4 occupation requests (access requests) issued from any ones of the interfaces to the access control bus BUS3 and to control and mediate the occupation right (access right) therebetween.
The operation of such a packet switching node will be briefly explained in the following.
Assume now that any one of the terminal interfaces 10 receives a calling packet from the associated packet terminal. Then the terminal interface, when receiving the calling packet, first sends an interrupt request to the node controller 30 through the interrupt control bus BUS1.
The node controller 30 in turn, when confirming the received interrupt request, gets access to the respective terminal interfaces 10 through the control bus BUS2 to check calling data (including a party destination number, a window size (the number of data which a terminal can send without permission of the associated terminal interface, i.e., without causing any buffer overflow), and so on) which are already registered at that time in a calling data memory (not shown) incorporated in each of the terminal interfaces. After having confirmed the calling data, the node controller 30 sends out the access request of the data bus BUS4 onto the access control bus BUS3.
The access request outputted thus onto the access control bus BUS3 is taken in the bus access controller 40, which in turn determines the then destination of the access right to be transferred under its control and mediation of the access right.
The node controller 30, only when obtaining the data bus access authority through such control and mediation of the bus access controller 40, transfers the connection request packet to the line interface 20 through the data bus BUS4. The line interface 20, when receiving the connection request packet from the node controller 30, prepares the received connection request packet in the same manner as for the data packet and transmits it to the associated multiplexing line.
The line interface 20, when transmitting the connection request packet and thereafter receiving a packet indicative of (informing) a connection approval or disapproval from the party packet terminal of the party node as an response to the transmission of the connection request packet, sends the response packet to the node controller 30.
The node controller 30, when receiving the response packet indicative of, for example, a connection approval, creates a connection table indicative of logical connection state between the line and terminal interfaces 20 and 10 in memories (not shown) provided within the interfaces 20 and 10 through the control bus BUS2, and sends the connection-approval informing packet to the corresponding terminal interface.
The terminal interface, when accepting the connection-approval informing packet from the node controller 30, further sends the accepted packet to the packet terminal which issued the aforementioned calling packet. This results in that the packet switching node is shifted to its data transfer phase.
In the data transfer phase, a data packet is sent from the terminal interface to the associated line interface logically connected thereto through the data BUS4.
At this time, the sent data packet has such a configuration as shown in FIG. 2.
More in detail, the data packet shown in FIG. 2 consists of a header field H and a data field D. Attached to the header field H is a connection data (connection identifier) of the data packet in question based on the logical connection contents of the connection table created by the node controller 30. Stored in the other data field D is the data contents of the data packet concerned.
The line interface, when receiving the data packet thus sent from the associated terminal interface, temporarily stores the received data pack in FIFO buffer (not shown) provided therein and at the same time, sequentially transmits the stored data to the associated multiplexing line.
When the communication between the caller and receiver packet terminals is completed and it is desired to cut off such a connection state therebetween, the same operation as in the previous connection request is executed except that the contents of the created connection table are deleted.
A relationship between the interconnection of the caller to receiver packet terminals and the connection table will next be detailed by referring to FIG. 3.
In the drawing, reference symbols 1A and 1B denote packet format terminals (which will be sometimes referred to merely as the packet terminals PT, hereinafter) in question, 2A to 2D denote non-packet format terminals (which will be sometimes referred to as merely as the non-packet terminals NPT, hereinafter), 3A to 3F low rate lines, 4A and 4B switches for selecting packet transmission lines established through the buses BUS1 to BUS4, reference numeral 5 multiplexing lines, respectively. In addition, reference symbols 11A, . . . 1nA, 11B, . . . and 1nB denote terminal interfaces (which correspond to the aforementioned terminal interfaces 10 in FIG. 1) in illustrated both nodes, and 21A and 21B denote line interfaces (which correspond to the aforementioned line interfaces 20 in FIG. 1) in the both nodes, respectively.
In the illustrated example, board addresses BA unique to the associated boards housed in the corresponding nodes are set to the terminal interfaces 11A, . . ., 1nA, 11B, . . . and 1nB respectively.
The terminal interfaces 11A and 11B are connected with the associated packet terminals (PTs) 1A and 1B, have logical channel numbers LCN and access channel numbers ACN set thereto respectively. The logical channel numbers LCN indicate the numbers of logical channels connecting these packet terminals 1A and 1B respectively; while the access channel numbers ACN, which correspond to the logical channel numbers LCN in a 1:1 relation, indicate connection relationships between the line interfaces 21A and 21B respectively.
Meanwhile, the terminal interfaces 1nA and 1nB, which are connected with the associated non-packet terminals (NPTs) 2A to 2D, have physical channel numbers PCN and access channel numbers ACN set thereto respectively. The physical channel numbers PCN indicate the numbers of physical channels connecting these non-packet terminals 2A and 2B respectively; whereas the access channel numbers ACN, which correspond to the physical channel numbers PCN in a 1:1 relation, indicate connection relationships between the line interfaces 21A and 21B respectively.
Similarly to the aforementioned terminal interfaces, the line interfaces 21A and 21B have board addresses BA unique to the associated nodes and access channel numbers ACN indicative of connection relationships with respect to the associated terminal interfaces. Also set, in particular, to these line interfaces 21A and 21B are transport channel numbers TCN which are uniquely determined with respect to the respective adjacent nodes.
In FIG. 3, the logical channel number LCN is denoted by "L", the access channel number ACN by "A", the physical channel number PCN by "P", the transport channel number TCN by "T", respectively. For the simplicity of the drawing. In addition, node controllers, bus access controllers and so on associated with the both nodes are omitted.
Here consider a logical channel connection between, for example, the packet terminals (PTs) 1A and 1B. Then the logical channel (LCN) of the packet terminal 1A is sequentially associated with one of the access channels (ACN) of the terminal interface 11A, with one of the access channels (ACN) and one of the transport channels (TCN) of the line interface 21A, with one of the transport channels (TCN) and one of the access channels (ACN) of the line interface 21B, with one of the access channels (ACN) of the terminal interface 11B, and finally with the logical channel (LCN) of the packet terminal 1B. Thus, it will be appreciated that, the connection relationship between the packet terminals can be completely described in terms of roughly three sorts of connection data, i.e., intra-node, transport and intra-node connections as shown in FIG. 3.
More specifically, in the case where it is considered to transmit a packet from the packet terminal 1A to the packet terminal 1B, when the following relationships (a) to (g) are determined, the relationship between the packet terminals 1A and 1B in question can be uniquely specified.
(a) A relationship between the logical channel number LCN of the packet terminal 1A and the access channel number ACN of the terminal interface 11A. PA1 (b) A relationship between the access channel number ACN of the terminal interface 11A and the access channel number ACN of the line interface 21A. PA1 (c) A relationship between the access channel number ACN of the line interface 21A and the transport channel number TCN used between the line interfaces 21A and 21B. PA1 (d) A relationship between the transport channel number TCN used between the line interfaces 21A and 21B and the access channel number ACN of the same interface 21B. PA1 (e) A relationship between the access channel number ACN of the line interface 21B and the access channel number ACN of the terminal interface 11B. PA1 (f) A relationship between the access channel number ACN of the terminal interface 11B and the logical channel number LCN of the packet terminal 1B. PA1 (1) The data packet is re-organized at the data copy unit CPY-A of the node A into 6 sorts of data packets which have the same data contents and which have the headers H containing connection identifiers corresponding to the 6 party destinations. PA1 (2) The 6 sorts of re-organized data packets are sequentially transferred or relayed to the target nodes having the specified packet terminals connected thereto, basically in accordance with such a procedure as explained in FIG. 3. PA1 (A) The occupation time of the switch 4A in the node A as a packet transmitter end becomes large and thus the delay time of communication in another connection becomes large. PA1 (B) Since it becomes necessary to transmit packets on the one-packet-to-one-connection basis though the packets have the same contents, the data copy unit CPY-A tends to become overloaded. PA1 (C) For the similar reason to the (B), the multiplexing-line occupation factor becomes high. For example, the multiplexing lines 51 between the nodes A and B or the multiplexing lines 52 between the nodes A and C must have a transmission band corresponding to 3 times the transmission band of the same packet. This largely prevents the utilization of the multiplexing lines in question in another communication to an unnegligible extent.
In this connection, it is common that the relationship between the logical channel number LCN and access channel number ACN in the each terminal interface is determined, in many cases, at the time of configuring the system; while the relationship between the access channel number ACN of the terminal interface and the access channel number ACN of the line interface as well as the relationship between the access channel number ACN and transport number TCN in the each line interface are determined every time when a calling connection is desired.
Therefore, when only ones of the relationships (a) to (f) which are determined every time at the time of the calling connection are described in the aforementioned connection table in the corresponding terminal or line interface, the connection relationship between the packet terminals 1A and 1B concerned can be logically and uniquely specified. The description of such connection relationship in the connection table is carried out under the node controller 30 (see FIG. 1) of the associated node as already explained earlier.
Each time the data packet is actually transferred, the terminal or line interface, when receiving the data packet, checks whether the data packet is directed to its own board. When the terminal or line interface determines the data packet directed to its own board, it sequentially rewrites the contents (such as the aforementioned channel numbers LCN, ACN and TCN and so on) of the connection identifier attached to the header H (see FIG. 2) of the data packet in question and also the aforementioned board address BA, on the basis of the contents described in its own connection table. Such operations are sequentially repeated.
At the end of the communication, the node controller 30 of the associated node sequentially erases the contents described in the connection table, whereby the connection relationship in question is released (disconnected).
In packet communication based on such packet switching network, there is sometimes carried out, in addition to the above 1:1 communication between the two packet terminals, such broadcasting packet communication that a packet is commonly transferred from one packet terminal to a plurality of other destination packet terminals at the same time, that is, in a 1:N relation.
FIG. 4 is a diagram for explaining how broadcasting communication is conventionally effected in the packet switching network.
More in detail, FIG. 4 shows a 1:6 broadcasting communication example wherein reference symbols 1A, 1B, 1C, 1D1, 1D2, 1E1 and 1E2 denote packet terminals (PTs) and a packet is to be transferred from the packet terminal 1A connected to a node A, to the packet terminal 1B connected to a node B, to the packet terminal 1C connected to a node C, to the packet terminals 1D1 and 1D2 connected to a node D, and to the packet terminals 1E1 and 1E2 connected to a node E.
Also included in FIG. 4 are terminal interfaces 11A and 12A in the node A, line interfaces 21A and 22A in the node A, a switch 4A in the node A, a terminal interface 11B in the node B, line interfaces 21B and 22B in the node B, a switch 4B in the node B, a terminal interface 11C in the node C, line interfaces 21C and 22C in the node C, a switch 4C in the node C, terminal interfaces 11D and 12D in the node D, a line interface 21D in the node D, a switch 4D in the node D, terminal interfaces 11E and 12E in the node E, a line interface 21E in the node E, a switch 4E in the node E, multiplexing lines 51 connected between the nodes A and B, multiplexing lines 52 connected between the nodes B and D, multiplexing lines 54 connected between the nodes C and E, and a data copy unit CPY-A provided in the caller node A to a copy the data field D (see FIG. 2) of a data packet to be transferred. Even in FIG. 4, node controllers, bus access controllers and so on associated with the respective nodes are omitted for the simplicity of the drawing.
Prior to execution of such 1:6 broadcasting communication, it is first necessary that the access channel numbers ACN issued from the terminal interface 11A (node A) of the calling terminal 1A should correspond to the associated 6 party terminals of call receivers.
To this end, in the illustrated example, when the caller terminal 1A issues a broadcasting communication request to the 6 packet terminals, the access channel numbers ACN issued from the terminal interface 11A are connected to the data copy unit CPY-A copy the data field D of the associated data packet through the data copy unit and also the access channel numbers ACN contained in the header H are rewritten so as to correspond to the 6 associated call receivers in the node A. The rewriting operation of such access channel numbers ACN also requires the use of a connection table (not shown) previously prepared in the data copy unit CPY-A. Through the copying operation of the packet data and the rewriting operation of the access channel numbers ACN at the data copy unit CPY-A, there are newly created 6 sorts of data packets which have the headers H containing connection identifiers corresponding to the 6 associated call receivers and also have the data fields D containing all the same contents. For the 6 data packets thus created, for example, such 6 connections as shown in FIG. 4 are established between the line interfaces 21A and 22A of the node A.
In the nodes (nodes B to E in the illustrated example) connected with the specified party packet terminals, connections between the line interfaces 21A and 22A and the packet terminals controlled by the respective nodes are set in the corresponding connection tables in response to a call indicative of the broadcasting communication request from the packet terminal 1A through the node A. As also shown even in FIG. 4, in the nodes (node B for the relay of the data packet to the node D and node C for the relay of the data packet to the node E, in the illustrated example) necessary for the relay of the data packet, such a connection as to pass the data packet therethrough toward the relay target node is also separately set in the corresponding connection table.
In this way, through the above connection setting processing at the associated nodes (nodes A and B to E), the single data packet issued from the caller terminal 1A is processed as follows.
In this manner, the 6 re-organized data packets eventually reach the 6 packet terminals 1B, 1C, 1D1, 1D2, 1E1 and 1E2 as transfer destinations.
In such broadcasting communication as mentioned above, when it is desired to transfer a common data to a plurality of destination packet terminals at the same time, the need for the execution of the every-time separate calling procedure can be eliminated. However, when it is desired to establish a connection between nodes or packet terminals as the broadcasting communication, it is necessary to establish 1:N connections at the data copy unit CPY-A and to transfer the packets on the established-connection basis, whether the connections are established logically or physically. For this reason, such a prior art packet communication system has had the following problems (A), (B) and (C), when explanation is made, for example, in connection with the example of FIG. 4.